1. Field of Invention
Aspects of the invention relate to an electrostatic capacitance detection device that reads the surface contours of a fingerprint or other target object having extremely small ridges and valleys, by detecting electrostatic capacitance, which changes according to the distance from the surface of the target object.
2. Description of Related Art
As described in, for example, Japanese Unexamined Patent Publication Application No. Hei 11-118415, No. 2000-346608, No. 2001-56204, No. 2001-133213, and so forth, in related electrostatic capacitance detection devices that are used in fingerprint sensors and so forth, a sensor electrode and a dielectric layer deposited on the sensor electrode are formed on a single-crystal silicon wafer. The principle of operation of a related electrostatic capacitance detection device is shown in FIG. 1. One of a pair of electrodes in a capacitor is a sensor electrode, the other is grounded to a human. Further, a dielectric layer is formed on the uppermost surface of the electrostatic capacitance detection device. The capacitance CF of this capacitor changes according to the ridges and valleys in a fingerprint contacting the surface of the dielectric layer. On the other hand, the semiconductor substrate is equipped with a capacitor that forms an electrostatic capacitance CS. These two capacitors are connected in series, and a predetermined voltage is applied. The application of a voltage causes a charge Q corresponding to the ridges and valleys in a fingerprint to be formed between the two capacitors. This charge Q is sensed using ordinary semiconductor technology and the surface contours of the target object are read.